1. Field of the Invention
The present general inventive concept relates to an apparatus to generate high voltage and a method thereof. More particularly, the present general inventive concept relates to an apparatus to generate high voltage by digital control using an application-specific integrated circuit (ASIC) on a control part and a digital control method thereof to control output stabilization and various output.
2. Description of the Related Art
An image forming apparatus prints an image corresponding to an original image data input on a recording medium, such as a printing paper. The image forming apparatus includes a printer, a copy machine or a facsimile. An electro-photographic method is employed in the image forming apparatus, such as a laser beam printer, an LED Print Head (LPH) printer, and a facsimile. The image forming apparatus using the electro-photographic method performs printing through charge, exposure, development, transfer and fixation steps.
FIG. 1 schematically illustrates a conventional image forming apparatus using an electro-photographic method. Referring to FIG. 1, the image forming apparatus using the electro-photographic method includes a photoconductive drum 1, a charge roller 2, a laser scanning unit (LSU) 3, a development roller 4, a transfer roller 5, a controlling part 6 and a High Voltage Power Supply (HVPS) 70.
The conventional image forming apparatus using the electro-photographic method performs printing steps as follows. The HVPS 70 supplies a predetermined voltage to the charge roller 2, the development roller 4, and the transfer roller 5 according to control by the controlling part 6. The charge roller 2 evenly electrifies a surface of the photoconductive drum 1 with a charge voltage supplied from the HVPS 70. The LSU 3 scans light (e.g., laser beam) corresponding to an image data input from the controlling part 6 to the photoconductive drum 1. Accordingly, an electrostatic latent image is formed on the surface of the photoconductive drum 1. A toner image is formed based on the electrostatic latent image formed on the surface of the photoconductive drum 1, using toner supplied by the development roller 4. The transfer roller 5 is driven by a transfer voltage supplied from the HVPS 70 and transfers the toner image formed on the photoconductive drum 1 to a recording paper. The toner image transferred to the recording paper is fixed on the printing paper by high heat and pressure of a fixer (not shown), and the printing paper is ejected to an outside of the conventional image forming apparatus in an ejection direction (not shown).
As a key part of the image forming apparatus, such as a copy machine, a laser beam printer or a facsimile, the HVPS 70 supplies voltage by instantaneously converting a low voltage of 12˜24V to a high voltage of hundreds or thousands volts and charging the drum of the image forming apparatus. The HVPS 70 is used as a constant voltage or current source to provide a required voltage or current.
FIG. 2 is a circuit diagram illustrating a conventional HVPS. Referring to FIG. 2, the conventional HVPS includes a low pass filtering part 10, a voltage controlling part 20, an oscillator and power transforming part 30, a voltage dividing part 40, a voltage sensing part 50 and a protecting part 60. When the low pass filtering part 10 receives an input signal D(t) that is a PWM (Pulse Width Modulation) signal from an external engine controller, a level of an output voltage is decided according to a duty ratio, and the low pass filtering part 10 converts the input signal D(t) into a DC signal through an RC 2-step filter having resistors R1, R2, R15 and capacitors C, and C10. The DC signal is used as a reference signal to control an output voltage of the HVPS 70.
The voltage controlling part 20 is operated as a controller having a difference circuit IC1 in parallel to a resistor R3 and a capacitor C2 to amplify an error signal, and compares the DC signal output by the low pass filtering part 10 and a signal having an actual voltage fed-back signal, to generate a driving signal of a transistor Q of the oscillator and power transforming part 30. The oscillator and power transforming part 30 controls a base current of the transistor Q based on the driving signal VT1 supplied by the voltage controlling part 20 through the resistors R4 and R5, and voltages between an emitter connected between R4 and R5 connected through a capacitor C3 and a collector of the transistor Q change using a voltage Vcc. Accordingly, a voltage VT2 of a first (primary) coil N2 of a voltage transforming part is determined, and a second voltage is induced in a second (secondary) coil N3 of the voltage transforming part having a high turn ratio.
The voltage dividing part 40 uses diodes D1 and D2 to rectify the secondary voltage and capacitors C4 and C5 to distribute and smooth the rectified voltage, and generates a final DC high voltage from an AC voltage (i.e., the secondary voltage) induced in the second (secondary) coil of the oscillator and power transforming part 30. The voltage sensing part 50 includes the resistors R16, R8 and R7 an integrated circuit IC2 in parallel with an RC filter made of a resistor R10 and a capacitor C7. The voltage sensing part 50 is connected to the protecting part 60 through resistors R11, and R12 and capacitor C8, and the protecting part 60 includes an integrated circuit IC2, diodes D3 and D4, and resistors R15, and R13. The voltage sensing part 50 and the protecting part 60 detect the final DC high voltage actually output, generate a feedback signal to the voltage controlling part 20 and prevent supplying an abnormal voltage.
The conventional HVPS illustrated in FIG. 2 is a circuit generating a high voltage to a development unit of one particular channel, and requires respective channels for supplying a predetermined high voltage to the charge roller 2, the development roller 4, and the transfer roller 5.
The conventional HVPS uses an analogue control method for individually and precisely controlling an output of each channel, and accordingly, errors caused by characteristic deflection between the low pass (RC) filter 10 and the voltage controlling part 20 should be corrected. The use of many components is a hindrance to cost-savings and the conventional HVPS may operate erroneously due to defective unit parts as a result of external factors. The transistor Q is used as switching device of the oscillator and the voltage transforming part 30 and always operates in a linear area, such that the transistor continuously generates heat. As illustrated in FIG. 2, the conventional HVPS uses many components, accordingly increasing manufacturing time during an assembly process, and requiring Printed Circuit Board (PCB) space for disposing the many components.